1. Field of the Invention
The present invention relates to a field-effect transistor (FET) and more particularly a normally-off type FET including a heterostructure of nitride semiconductor layers.
2. Description of the Background Art
A conventional FET using a group III-V compound nitride semiconductor includes a heterostructure of a GaN layer and an AlGaN layer on a substrate (see Patent Document 1: U.S. Pat. No. 5,192,987). Here, the AlGaN layer has a smaller lattice constant than the GaN layer.